When adding a custom module with a name, e.g.:
```jsonc
{
...,
"custom/foo#bar": { },
...
}
```
The custom module does not retain the `bar` class as it should, because
all the classes are replaced with the runtime output:
1b4a7b02f4/src/modules/custom.cpp (L141-L147)
Avoid removing the module instance name class so css class behavior is
consistent between all modules.
458c03bf95